Composition of asynchronous functions in javascript

compose.js

export default function compose(...fns) {
    return async x => {
        let res = x;
        for (const fn of fns) {
            res = await fn(res);
        }
        return res;
    } 
}

// Example of usage
// const f1 = x => {
//     return new Promise((resolve, reject) => {
//         setTimeout(() => {
//             resolve(x * 2);
//         }, 500);
//     });
// }

// const f2 = x => {
//     return new Promise((resolve, reject) => {
//         setTimeout(() => {
//             resolve(x + 3);
//         }, 100);
//     });
// }

// (async () => {
//    const f = compose(f1, f2);
//    const value = await f(7); // ((7 * 2) + 3)
//    console.log(value); // 17
// })();